Hi Marta, Welcome to the forum. I have a few questions. Do you suffer from panic attacks while you are under stress. Hyperventilating can cause numbness and tingling in all areas of the body and usually starts around the mouth and on face. Although, I am unsure why only one leg.
Does it go away when you calm down or is it continual? Have you seen a doctor yet? Are you on any medications? Some medications can cause this.

It may all be related to the stress but you should see a doctor to rule out other things.
There are many knowlegable people on this site who probably have many more ideas and questions for you.
I hope this helps!